ZEN-M-KIT, phone, problem

Make: Mercedes-Benz Model: GLS Year: 2018
ZEN-M-KIT S/N 189295

Problem: the volume of the outgoing call and the volume of the interlocutor's voice are maximum.

If use the volume control HU, then with one step of regulation, the volume of the outgoing call and the voice volume of the interlocutor are abruptly set to the level selected in the MB system settings.

Help me

Dear NAV-TV,

Have the same issue with NAV-TV Zen-M as described below in my Mercedes-Benz GLC250 (2017 yb)

A problem reveals in two similar situations:
1. when I have an incoming phone call (cell phone is connected via Bluetooth) and press a button to answer, the speakers voice goes with enormous volume level which is hard to resist;
2. when I make an outgoing call from the car, the dial phone beep also goes with the similar volume level seems like maximum possible a system can provide. It is impossible to stay inside the car.

However, I would like to admit when connected via Bluetooth music plays with normal sound level. Other sources also play correct using the Zen-M device.

Will highly appreciate if you could resolve this issue promptly. Look forward to receiving feedback from you.

please provide the serial numbers of the units.

Order# WS001989
Serial# 189295

Serial No. 193942